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A space colony that resembles the design of a Stanford torus generates artificial gravity by centripetal force.

Discussions about benefits of such fake gravity can be easily found: no more constant physical exercise like in today's space ships (you can concentrate on your mission); many activities that are not possible in today spaceships may be possible with artificial gravity.

Discussions about differences with real gravity can be found too: some say that if you throw up a coin, it won't describe the same curve as in Earth. Due to the rotational velocity of the torus, the coin will fall down and towards the direction opposite to the torus rotation.

If we cannot return to Earth:

How many generations are needed for any change to start to show? Of what might those changes consist?

colony divisions

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    $\begingroup$ I can imagine cultural, but not biological changes. Especially if you keep always gravity to ours. Or what gravity will there be? $\endgroup$ – Pavel Janicek Nov 14 '14 at 12:51
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    $\begingroup$ I think you are assuming that gravity is a real thing that needs to be 'emulated' in the space station. Gravity is a fictitious force that we invoke to explain the accelerated frame caused by (the distortion of space around) matter (like, a planet). The toroidal space habitat creates an accelerated frame. Neither one is fake or emulated, they are both accelerated frames. $\endgroup$ – Spike0xff Nov 14 '14 at 18:18
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    $\begingroup$ @Spike0xff While General Relativity is our most accurate description of gravity, it is the theories of quantum gravity that are being developed with the aim of unification. In these theories, gravity is not a fictitious force, but a physical force mediated by massless particles called gravitons. $\endgroup$ – Epsilon Nov 15 '14 at 3:34
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    $\begingroup$ @NPSF3000 Its just an early concept of the colony, many changes will be made before its final shape is decided. I will consider moving the red R&D. $\endgroup$ – Hatoru Hansou Nov 15 '14 at 14:09
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    $\begingroup$ @HatoruHansou: It is very much the same as in an airship, and it doesn't depend a lot on the speed (you missed the sarcasm in my commment). 1 RPM or 50 RPM, pretty much the same, it makes no difference. Any object you toss obeys Newton's first law of motion. The only thing that won't move "normally" is the air (laminar flow, slower near the center), but unless the rooms are extremely high, you will hardly notice the difference other than having ventilation "for free". The measurable drag on a coin or such will be zero. $\endgroup$ – Damon Nov 15 '14 at 19:38
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The point of the rotation is to emulate earth level gravity, so you should not expect to see any large scale changes.

Where you would see changes though is in balance and rotational expectations. As you already mentioned the thrown coin would fly "wrong". You would also see this when running, turning corners, standing, etc though.

Depending on the size of the torus these effects may be smaller or larger though, for example the wikipedia article on this sort of space station says that:

Turning one's head rapidly in such an environment causes a "tilt" to be sensed as one's inner ears move at different rotational rates. Centrifuge studies show that people get motion-sick in habitats with a rotational radius of less than 100 metres, or with a rotation rate above 3 rotations per minute. However, the same studies and statistical inference indicate that almost all people should be able to live comfortably in habitats with a rotational radius larger than 500 meters and below 1 RPM. Experienced persons were not merely more resistant to motion sickness, but could also use the effect to determine "spinward" and "antispinward" directions in the centrifuges.

So as long as the station was sufficiently large humans would see very few effects and would quickly acclimatise.

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    $\begingroup$ Let's say that these people have adapted to the point of being able to safely run and jump. I'm assuming here that such adaptation is possible. I'm about to accept this answer. $\endgroup$ – Hatoru Hansou Nov 14 '14 at 13:47
  • $\begingroup$ I calculated 0.4229810233 RPM by the formula given at Wikipedia for 5000 meters of diameter. So maybe no adaptation at all is needed. I still expect that a native of this colony feel weird if suddenly placed on Earth. $\endgroup$ – Hatoru Hansou Nov 14 '14 at 13:53
  • $\begingroup$ Basically the bigger the station the smaller the effect. I'd wait a while before you accept the answer though, a better one may come. $\endgroup$ – Tim B Nov 14 '14 at 14:07
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    $\begingroup$ More of an addition than anything, as this answer explains things rather well: Some people could be rather well-suited to changing gravity in such a station perhaps, if they have to move towards the centre for technical work, such as repairs or maintenance, or simply getting across the station more quickly (5km station diameter = ~15-16km circumference). Since the force felt is based on their radius from the axis, as they move "up" the gravity felt would change significantly, no? Sounds like an interesting job, or a fun way to travel quickly! $\endgroup$ – Crabgor Nov 14 '14 at 17:07
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    $\begingroup$ Yes, that's right. Moving "up" towards the center you would both grow lighter and feel a force pushing you sideways. This is one reason the large size is needed, otherwise you'd experience noticeably different forces on your head and your feet - and just standing up would throw you sideways. $\endgroup$ – Tim B Nov 14 '14 at 17:54
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A space-faring civilization is beyond the point in history where the environment exerts much evolutionary pressure on the species (that's why our eyes get worse and we have allergies -- imagine that in front of the tigers or mastodons 15000 years ago). Perhaps gravity high enough to prevent moving around (and thus sexual intercourse) in physically weak individuals would favour reproduction of strong individuals; but then reproductive medicine makes intercourse superfluous anyway. Plus chances are that space dwellers are naturally infertile anyway because of radiation exposure, so high gravity wouldn't favour anybody anyway.

Edit: Since you are hinting in a comment that you aimed at the difference between "emulated" and "natural" gravity: these are misconceptions. Gravity is a curvature of space time, whether by "acceleration" or by "being in a gravity field" -- the difference between both is just a difference in the point of view, as the theory of general relativity states. The famous person in the falling elevator (read: closed system) cannot tell whether s/he is in zero gravity or in free fall on earth. It's physically indistinguishable, it is identical. In the same way a person in an accelerating elevator could not tell whether they are accelerating in zero gravity or standing still in a gravity field. It's physically identical. None of them is more or less emulated or natural.

That said, of course a circular motion "curves space time" for the dwellers in a way that they perceive somewhat different accelerations when they move (the coriolis forces) than on earth; but that is a (quantitative) difference in vector, not an essentially different affair which would influence people or affect our genes. Unless you have a tendency to become dizzy when you move quickly forward and backward -- that might decrease your reproductive chances in a space station ;-).

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    $\begingroup$ I appreciate the clarification and I like how it is written. By maintaining in sight that gravity is a curvature of the space-time (Einstein?) somehow the Stanford torus way of provide gravity seems pretty safe. About radiation exposure: let's pretend these people already have a solution for that. $\endgroup$ – Hatoru Hansou Nov 14 '14 at 22:04
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The bigger the habitat, the less difference there will be, since Coriolis effects decrease with lower RPM, and a bigger habitat can rotate more slowly and still have 1g at the rim.

I think the biggest difference will be that gravity will be variable, with the highest gravity at the rim of the hab, decreasing as you head towards the center, and zero at the hub. That means that people can spend part of their day in normal G, and part in low or no G, depending on the activities they're doing.

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All of this reasoning surrounding this scenario presupposes the similarity between actual gravity due to a mass, and the angular velocity and moment of inertia due to the torque of the rotating torus; of which there IS no comparison.

Gravity sucks, and Torque pushes (or blows :p ), so any perceived "symptom" of gravity would be a placebo, initiated and sustained by continuous contact with the rotating body.

Necessarily, one would need not to leave the inside surface of the torus to benefit from the simulation of gravity. If one were to say, reach out over the side, they would be jettisoned outward along the Force vector F.

Human nature being what it is, and more curious than cats; to answer the Question in the OP: "How many generations are needed for any change to start to show?" -

Answer: This is immeasurable, or equal to the Null Set, as no population would reside on the torus long enough to find out. (this is akin to asking the age-old Tootsie Pop question.) Also, to suppose there could be a fool-proof method of containing said Curious Adventurers, we need only refer to Murphy's Cathode-Ray Corollary which states that "A $500 picture tube will always protect a 50¢ fuse by blowing first".

tl:dr version:

Answer = i/0

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  • $\begingroup$ All true. That why I think that we can speak of a simulated gravity and a real gravity (Earth's). This is for a video game project of mine. People live in colonies because they do not have the option to go back to Earth. If they cannot stand it their options are: to improve their colony, to build another somehow (by using materials from asteroids, other planets, etc) and then move to the new one. $\endgroup$ – Hatoru Hansou Nov 14 '14 at 22:38
  • $\begingroup$ I know we cannot really know what may happen to humans if forced to live in colonies with artificial gravity. Speculative answers are ok in this context. I want more sophisticated speculations than the ones I capable of. General consensus is that nothing of interest will happen to those people (at least due to gravity) and that is what I accepted. $\endgroup$ – Hatoru Hansou Nov 14 '14 at 22:44
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List of very quickly recognizable symptoms

  • Weakness
  • Unusual blood from unusual bone marrow
  • Increased height
  • Lower real-gravity tolerance
  • Clumsiness?

List of later symptoms

  • Radioactivity protection
  • Giantism
  • Mental patterns associated with small spaces
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  • $\begingroup$ Giantism, If it's mean taller people, isn't prevented by an artificial gravity adjusted to be the same as in Earth? $\endgroup$ – Hatoru Hansou Jan 31 '16 at 5:23
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We already have examples of people living for long periods of time in places that have even bigger differences in gravity (compared to that experienced by ground pounders): ocean-going vessels.

As far as I know, there are practically no differences between people whose families have been sailing the seas for centuries, vs. people whose ancestors have been walking on land for generations.

Of what might those changes consist?

Perhaps in space, everyone talks like a sailor? :-)

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    $\begingroup$ Remember that this is emulated gravity. Planet Earth has the gravity It has due to Its mass. I thought somebody may have something to say on emulated gravity vs Earth gravity, but It seems everybody think emulated gravity is functional equivalent to Earths and a safe replacement. Ok, It's an answer. Actually, I thought that too, but I wanted to see if there was something else I was not aware of. $\endgroup$ – Hatoru Hansou Nov 14 '14 at 15:52
  • $\begingroup$ @HatoruHansou So far as we are aware there are no differences. We won't really know until we try it for real though! $\endgroup$ – Tim B Nov 14 '14 at 17:55
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    $\begingroup$ @HatoruHansou the main result of the special theory of relativity is that "gravity" due to acceleration and "gravity" due to a massive body are indistinguishable. When the acceleration is due to rotation then you can detect the rotation, and it has some effects, but not very important ones for the most part. $\endgroup$ – hobbs Nov 15 '14 at 3:00
  • $\begingroup$ (Oops, my mistake, general relativity deals with acceleration; special relativity is only for inertial frames) $\endgroup$ – hobbs Nov 15 '14 at 4:36
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I'm not sure if emulated gravity would have much effect, but the overall strength of gravity would certainly have one.

If the gravity was weaker, then the people on board would be weaker as well. The density of their bones would also be less, so they would be frail compared to an earthling. If they did go back to Earth, they would have a hard time moving around. There may be some other health related effects as well which could shorten their lifespan. How much of a change would be anyone's guess.

On the other hand if the gravity was stronger, than the people born there will grow to be stronger than the average earthling. They would be able to do great feats of strength on Earth and generally make everyone else look like a weakling.

These effects would be present in the first generation born there, or to people who have spent a very long time there.

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  • $\begingroup$ That's the reason to have a gravity as similar as possible to Earth. But this gravity is not generated in the same way. So I thought, what may happen to humans if evolving with such a gravity? In theory, as they weight the same or very close to what they weighted on Earth, then things like their bones getting weaker should not happen. $\endgroup$ – Hatoru Hansou Nov 14 '14 at 19:44

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